1. Field of the Invention
The present invention relates to a thermoplastic vulcanizate prepared from a high performance engineering thermoplastic polymer such as polyurethane and a chlorosulfonated polyolefin and/or a chlorinated polyolefin; to a high performance hose such as a power steering hose constructed from such thermoplastic vulcanizate material; and to a method for the manufacture of such high performance hoses.
2. Description of the Prior Art
Hoses, particularly curved hoses, typically, are manufactured by positioning a pre-cut length of uncured hose over a curved mandrel and then heating the mandrel and curing the hose so that the hose retains its desired shape. The hose may solely be an elastomeric tube or it may be surrounded or have incorporated therein a twined reinforcement. Optionally, a cover may surround the hose. Typically, the hose is made by extruding a tube of heat curable elastomer. The hose is then placed over the mandrel which is heated to cure the inner layer next to the mandrel. The cured hose is then removed from the mandrel while the mandrel is hot to facilitate easy removal of the cured hose from the mandrel. One such method is described in U.S. Pat. No. 4,537,736 to Peltzman et al. Such rubber hoses have been used in a wide variety of applications such as fuel feed hoses, torque converter hoses, air conditioner hoses, power steering hoses, etc. However, in general, rubber surfaces do not exhibit high resistance to chemical attack and prior art attempts have failed to increase the chemical resistance beyond certain limits. For example, U.S. Pat. No. 5,476,121 to Yoshikawa et al discloses rubber hoses having improved barrier and flexibility performance by providing an inner tube of a synthetic resin having an outer peripheral surface, forming a thin film of silver or a silver base alloy on the outer surface of the inner tube, and heat curing a rubber layer to the thin film through an adhesive layer.
High performance hoses such as power steering hoses require high resistance to both chemical and temperature degradation. At present, power steering hoses and other high performance hoses are made from compounded elastomers such as a chlorinated polyethylene, a chlorosulfonated polyethylene or similar materials capable of withstanding temperatures up to 300° F. and the chemical effects of power steering fluids. Chlorine-containing polyolefins including chlorinated polyethylene and chlorosulfonated polyethylene generally possess good mechanical properties, good compression set, good low temperature flexibility and good dynamic fatigue resistance. These materials also exhibit excellent aging, weathering, chemical and ozone resistance due to their saturated backbones. However, in order to withstand high temperatures of about 300° F. and chemical resistance to power steering fluids, hoses constructed of such materials must be built and vulcanized on a mandrel and then removed from the mandrel for additional processing. A method for the manufacture of power steering hose on a mandrel is further described in U.S. Pat. No. 3,972,757 to Derderian et al. In view of the cost associated with manufacturing high performance hoses such as power steering hoses, it is desirable to provide materials having the desired characteristics but which are easily formable without the use of a mandrel while providing improved performance and reduced overall costs.
U.S. Pat. No. 5,683,773 to Kemper teaches an automotive hose where the inner tube or, preferably, the cover portion is formed of an elastomer comprising a chlorinated polyethylene-based elastomer or polyether-based elastomer stabilized with barium sulfate.